1. Field of the Invention
The present invention relates to carbonless copying systems.
2. Description of the Prior Art
Carbonless copying systems usually include a plurality of paper sheets or substrates arranged in a manifold set, each sheet of the set having one or more coatings on its surfaces. The manifold set is designed so that when a marking pressure caused by a typewriter, pen, or other instrument is applied to the outermost sheet, a colored mark will be formed on at least one surface of each sheet of the manifold set.
To this end, the top sheet of the manifold set to which the marking pressure is applied with a coating on its back surface. This coated back surface includes microcapsules containing an initially colorless chemically reactive color-forming dye precursor as the fill material. The upper surface of the next sheet, which is adjacent to the back surface of the top sheet, is coated with a material containing a component, such as phenolic resin or reactive clay, that is capable of reacting with the colorless dye precursor contained in the microcapsules to produce a color. Thus, a marking pressure on the upper surface of the top sheet will rupture the microcapsules on the bottom surface and release the colorless dye precursor. The colorless dye precursor then chemically reacts with the reactive component of the coated front of the lower sheet to produce a colored mark corresponding to the area of marking pressure. In similar fashion, colored marks are produced on each succeeding sheet of the manifold set by the marking pressure rupturing the microcapsules carried on the lower surfaces of each sheet.
The sheets of the manifold set in carbonless copying systems are designated in the art by the terms CB, CFB, and CF, which stand respectively for "coated back", "coated front and back", and "coated front". The CB or transfer sheet is usually the top sheet of the manifold set and the sheet upon which the marking pressure is applied. The CFB sheets are the intermediate sheets of the manifold set, each of which is able to have a mark formed on its front surface by a marking pressure and each of which also transmits the contents of ruptured microcapsules from its back surface to the front surface of the next sheet. The CF or recording sheet is the bottom sheet and is only coated on its front surface so that an image may be formed on it.
While it is customary to have the coating containing the microcapsules on the back surface of the sheets and to have the coating containing the reactive component for the capsules on the front surface of each of the sheets, a reverse arrangement is also possible. In addition, one of the reactive ingredients may be carried in the sheets themselves, rather than applied as surface coatings. Furthermore, the reactive component for the colorless dye precursor may be microencapsulated instead of or in addition to the precursor. Patents illustrative of the various kinds of systems that may be used in the production of manifold carbonless copying systems include by way of example: U.S. Pat. Nos. 2,299,694 (Green); 2,712,507 (Green); 3,016,308 (Macaulay); 3,429,827 (Ruus); and 3,720,534 (Macaulay et al.).
The microcapsules used in carbonless systems generally comprise a core of fill material surrounded by a wall or shell of polymeric material. The wall surround the fill material acts to isolate the fill material from the external environment. When it is desirable to release the fill material, e.g., the dye precursor, the capsule wall may be ruptured by mechanical pressure, for example, thereby introducing the fill material into its surroundings. Generally, microcapsules comprise separate and discrete capsules having non-interconnecting hollow spaces. The fill material is thus enveloped within the general continuous polymeric walls of the microcapsules, which may range from 0.1 to approximately 500 microns in diameter.
In carbonless systems it is desirable to obtain a strong image on the recording or CF sheet. One way of enhancing the image of a carbonless system is to increase the concentration of the dye precursor contained in the microcapsules coated on the CB sheet. However, this method of image enhancement suffers from a serious drawback in that dye precursors are generally quite expensive. Therefore, any increase in the concentration of dye precursor in the CB microcapsules necessarily increases the cost of the carbonless copy system. A second solution is to coat more dye containing microcapsules on the transfer or CB sheet. This, however, suffers from the same drawback as the first proposed solution since a greater amount of expensive dye precursor is used in the resulting carbonless system. Thus, there is a need for a carbonless copy system that produces an enhanced image without using an economically prohibitive amount of expensive dye precursor.
Microcapsules that contain only an organic solvent for use in carbonless copy systems are disclosed in U.S. Pat. Nos. 3,663,256 (Miller et al.) and 3,672,935 (Miller et al.). Both of these patents disclose at FIG. 2 (I, Ia, Vb, Vc, and Vd) the use of solvent-only capsules coated on the CB sheet of a manifold system or in a self-contained carbonless system. In each of these schematic diagrams neither of the two reactive mark forming components, i.e., the dye precursor and the clay, is microencapsulated. Thus, the solvent-only microcapsules shown in the Miller et al. patents are the only sources of solvent in these proposed carbonless systems.
The Miller et al. carbonless systems disclosed at FIG. 2 (I, Ia, Vb, Vc, and Vd) have not met with widespread commercial acceptance. Since microencapsulation is the surest means of isolating the mark forming components from each other prior to pressure imaging, the above systems increase the likelihood of inadvertent color develoopment that is a common problem in carbonless copy systems. Premature discoloration has been variously referred to as blush, offset, bluing, ghosting, and backprint. Whatever it is called, it is highly objectionable and undesirable in a carbonless copying system.
The following patent documents disclose various architectures known in the carbonless copying art. U.S. Pat. Nos. Re. 30,041 (Maalouf); Re. 30,116 (Maalouf); 4,003,589 (Konishi et al.); 4,071,469 (Vincent et al.); 4,096,314 (Cespon); 4,130,299 (Wygant); 4,147,830 (Kato et al); 4,187,233 (Petitpierre); 4,211,436 (Kuhlthau et al.); 4,250,098 (Chang); 4,287,074 (Earhart et al.); 4,295,662 (Tutty); 4,309,047 (Petitpierre); 4,316,036 (Petitpierre); 4,343,939 (Cesark et al.); 4,343,944 (Burri); 4,355,823 (Burri); 4,363,503 (Schmidt et al.); and 4,372,581 (Schumacher et al.); and United Kingdom Patient Specifications Nos. 1,290,369 (Fuji); and 1,417,206 (Mizusawa). None of the patents listed above discloses the use of microcapsules that encapsulate a fill material consisting solely of solvent.